Electronicdesign 29528 Mlx90821 Melexis Sensors Hres

Relative Pressure Sensor IC for EVAP Systems in ICEs, Hybrid Vehicles

Nov. 5, 2019
Melexis’ MLX90821 relative pressure sensor IC offers reliable measurement of fuel vapor pressure from 50 to 700 mbar.

Melexis' MLX90821 relative pressure sensor IC is designed for measuring low pressures in automotive applications. Using the latest MEMS technology, closely integrated with an analog signal chain and digital signal processing, the MLX90821 is a system-in-package IC solution for reliable measurement of fuel vapor pressure from 50 to 700 mbar, says the company. This makes the MLX90821 suitable for evaporation (EVAP) systems designed for internal combustion engines (ICEs) or hybrid vehicles.

Implementing fuel pressure vapor detection using so-called EVAP systems is increasingly important for automotive manufacturers, as more regions introduce strict legislations prohibiting the venting of fuel vapor to the atmosphere. As vapor builds up inside fuel tanks and crank cases, the EVAP systems are designed to capture, store, and responsibly dispose of the vapor, preventing it from escaping into the air. Pressure sensors that can operate at very low pressures are a crucial part of these systems, as they are able to detect even the smallest leaks that can potentially appear at any point in the EVAP system.

“The MLX90821 is a relative pressure sensor that has the range, reliability, stability, and accuracy to cover EVAP systems for both ICEs and hybrid engines,” said Laurent Otte, pressure sensors product line manager, Melexis. “This gives Tier 1 and module manufacturers the ability to standardize on a single design for both types of engines, using a sensor IC that is not only factory calibrated but can also be customized for each individual application. Its robust, easy-to-seal packaging is certified to operate between -40 and +150°C, and comes with full PPAP support.”

Fuel vapor pressure measurement is even more complex in hybrid vehicles, creating demand for more capable sensing solutions. Also, as EVAP systems in both ICEs and hybrid vehicles may feature several pressure sensor ICs, design flexibility and simplicity are critical.

According to Melexis, the MLX90821 is small enough to be used in modules of any size, offering a high level of integration through a system-in-package approach. This makes designing with the MLX90821 simple, providing what is essentially a "plug-and-play" approach, claims the company. While both analog and SENT outputs are provided, the DSP offers the ability to make full use of the SENT interface’s fast channel and slow channel, add diagnostic messaging, and apply custom calibration. The MLX90821 offers automotive diagnostic features such as clamping levels, broken track diagnostics, and multiple internal fault diagnostics.

The system-in-package approach uses a MEMS sensor, manufactured through back-side etching. This allows the sensing element to be exposed to the vapor or other media while providing protection against contaminants present in harsh environments like fuel vapor systems. The CMOS part of the system has been developed to deliver design flexibility, while the entire sensor offers high levels of EMC protection and immunity, making it simple to design into EVAP systems for both ICEs and hybrid vehicles, says Melexis.

Each sensor IC is calibrated during the final steps of manufacture, with the pressure transfer curve and clamping levels stored in the internal EEPROM. The measurement is provided through the ratiometric analog output or as a SENT output, which may also contain temperature measurements. An optional NTC temperature compensation feature makes use of an external NTC, which may be required when the application also needs to record an accurate temperature measurement of the media being monitored. Further configuration is possible using software tools provided and supported by Melexis.

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